It is indispensable for an electrical electronic component used widely in vehicles and electrical appliances to be electrically insulated from outsides for satisfying its use purpose. For example, an electrical wire is coated with a resin having an electrical insulation property. Today, applications in which electrical electronic components with complicated shapes are required to be packed in a small capacity, e.g., mobile phones, are sharply increased and in such a situation, various methods for their electrical insulation are employed. Particularly, in the case where an electrical electronic component having a complicated shape such as a circuit board is sealed with a resin serving as an electrical insulator, a sealing method for reliably following the shape of the electrical electronic component without leaving any un-packed portion is required. For that, it is common to employ a method for decreasing the viscosity of a sealing resin composition at the time of coating. A hot melt resin for sealing whose viscosity is lowered only by heating and melting to make sealing possible can be solidified to give a sealed body merely by cooling after sealing and thus has a high productivity, and in addition, since a thermoplastic resin is commonly used therefor, the resin can be melted and removed by heating after the life as a product is finished, thereby easily making recycling of the component possible.
Further, in vehicle applications, a heat generating body often exists in an electronic substrate installed in an engine room or the like, and therefore, a countermeasure of installing a heat releasing plate made of aluminum is taken in order to prevent heat storage. Still further, for making a wire harness for vehicles lightweight, shift from a copper wire to an aluminum wire has been promoted. In such a situation, a sealing material has been frequently required to have bond property to aluminum.
Having both a high electrical insulation property and water-proofness, a polyester is supposed to be a very useful material for the above-mentioned application; however, in general, a polyester has a high melt viscosity and it is necessary to carry out injection molding at a high pressure of several hundred MPa or more in the case of sealing a component with a complicated shape, and there is a risk of breaking an electrical electronic component. Patent Document 1 discloses an adhesive composition for a structure, containing a specified polytetramethylene glycol copolymerized polyether ester elastomer and an epoxy compound having at least 1.2 or more of glycidyl groups on a number average basis in the molecule. Herein, the polyester resin used herein has good initial bond property but tends to have high crystallinity, and thus generates strain energy at the time of transfer from the amorphous state to the crystalline state after bonding, and therefore, the bond strength tends to be lowered significantly and the polyester resin is unsuitable for a sealing material for electrical electronic components.
Patent Documents 2 and 3 propose a hot melt resin composition for sealing having a melt viscosity that enables sealing at a low pressure so as not to damage electrical electronic components. The resin composition allows molded components with good initial bond property to be obtained and allows a polyester-based resin composition to be applied to common electrical electronic components. However, the resin composition have a problem that if the resin composition is, for example, exposed to a cooling and heating cycle at −40° C. and 80° C., repeatedly many times for a long duration, the bond strength is rather considerably lowered and at the same time, the sealing state cannot be maintained in some cases.
Patent Document 4 discloses a resin composition for sealing electrical electronic components, in which a crystalline polyester resin, an epoxy resin, and a polyolefin resin are blended. This composition has a high adhesion strength and is durable for a cooling and heating cycle load; however, the composition has a problem that a blended product containing glycidyl may cause gelation and aggregation due to curing if stagnated under high temperature.
Patent Document 5 discloses that a hot melt adhesive composition in which a specified polyester resin and a phenol-modified xylene resin are blended shows a good adhesion property to tinned copper and a biaxially stretched poly(ethylene terephthalate) film. This adhesive composition also has a problem that the adhesion durability is insufficient to a cooling and heating cycle at −40° C. for 30 minutes and 80° C. for 30 minutes in automotive applications or the like.